Radioimmunotherapy (RIT) uses an antibody to deliver a relatively short lived isotope into close proximity with a tumor so the radiation emitted on decay (preferably a beta or alpha particle) has a very high probability of destroying cells in the tumor. It is an effective treatment for a variety of cancers. One key to expanding the use of RIT is the availability of additional isotopes that are compatible with other antibodies. This project develops a generator to deliver188Re (a beta emitter) on demand. The short half-life (16.9 h) of 188Re makes it possible to deliver large doses of radiation to the target with minimal harm to other tissues. 188Re is the decay product of 188W, present in the generator as tungstate on an inorganic anion exchanger. Inorganic ion exchangers are more radiation resistant than organic ones, and can be tailored to be specific for the desired ion. The anion exchangers in this project are synthetic hydrotalcites, such as Mg2AI(OH)7, and other structurally related compounds which are effective anion exchangers, such as LiAI2(OH)7. They have the necessary properties (high affinity for WO4= and low affinity for ReO4) for this application. These properties will be optimized by controllably varying the composition and crystallinity of the compounds.